How to convert $...$ to \(...\)

Question

So according to Why is \[ ... \] preferable to $$ ... $$? and Are \( and \) preferable to dollar signs for math mode? I should be using \(...\) instead of $...$ and \[...\] instead of $$...$$.

But what if I have a document where I've already used dollar signs a bit? How do I convert them? A simple find and replace won't work since:

1. It won't care whether $$ is a beginning or ending; and
2. I use the dollar sign in the text (to refer to the currency).

Does anyone have a neat tip for this?

Answer 1

Single $ are fine and supported syntax for inline math and even $$ are mostly OK for display math. They are bad style but most of the time (if you are not using fleqn) they will give the same output as \[..\] so you can just change $$ to \[ as part of general editing as you edit the formulae, if you are not confident with regular expression replaces there is no pressing need to do a global edit of the document which may do more harm than good if you get the regular expression wrong. So try to use \[ going forward but don't lose sleep over $$ already in your document:-)

Answer 2

This will depend a lot on which editor you use and the features it provides so I doubt there will be a single answer; however, if you editor has good regex support then this should be pretty easy.

Here's how you can match for $...$

/\s\$(.|\n)+?\$/g

and similarly, matching for $$...$$:

/\s\$\$(.|\n)+?\$\$/g

This will not match the dollar signs as they have to be escaped with \$ and the above pattern requires any of the whitespace characters before the dollar sign (space, tab or newline). You can see a nice visualization for that here and here respectively.

If your editor supports the s flag from Perl, then you can simplify (.|\n)+? to just .+? as . will match new lines too.

Finally, putting it together with a substitution, you get:

s/(\s)\$(.+?)\$/\1\(\2\)/sg

Note that I'm not escaping certain characters because it will depend on the particular implementation of regex. In particular, the group parentheses may require \(...\) and the +, ? and the backslashes in the replacement may also need to be escaped depending on which regex implementation you are using.

If you are in the command line and have Perl, then the following two commands should do the trick:

perl -077pi.bak -e 's/(\s)\$\$(.+?)\$\$/\1\\[\2\\]/sg' document.tex
perl -077pi.bak -e 's/(\s)\$(.+?)\$/\1\\(\2\\)/sg' document.tex

Note that this will not match anything at the very start of the file; however, I don't think this will be a big issue as the start of the file will typically be a comment or at least \documentclass.